Systems and devices using fluid pressure for lifting and holding heavy loads are known. These systems and devices typically include check valves, which prevent sudden and potentially damaging loss of load-lifting forces when the supply of pressurized fluid unexpectedly fails. Typically, the check valves are opened either by applying a lower pressure pilot fluid, or by applying manual pressure, sufficient to overcome the locking forces.
The amount of force required to open a check valve depends upon the area of the main check valve that is locked, and the magnitude of the locking forces. For example, to unseat a main check valve having a 0.75 inch diameter, which is seated at a locking force of 100 psi, about 44 pounds of opening force must be applied. This opening force is more than a typical operator can apply, either manually or using a solenoid. Furthermore, the application of this force using pilot fluid pressure requires the use of relatively large pilot pistons. The requirement of relatively high pilot pressure force imposes added wear and tear both upon the check valve and the pilot piston, which leads to reduced operating life. The requirement of large pilot pistons also increases the overall dimensions of the valve itself.
There is a need for pilot check valves requiring reduced operating forces, which, in turn, will lead to increased operating life. There is also a need for pilot check valves having a more compact size.